The present invention relates to a vibration drive utilizing a Piezoelectric vibration exciter, more particularly, to such a vibration drive which is mounted on a machine for producing shaped concrete bodies from a mold which is placed on a vibrating table and filled with flowable concrete.
Various forms of mechanical-electrical cam and eccentric motors have been used in order to cause the vibrating table of a molding machine to vibrate. In this manner, the mold which is generally open at the top and bottom and which is positioned on the vibrating table is similarly caused to vibrate to compact and to distribute as uniformly as possible the concrete mass which has been placed in the mold cavities.
The disadvantage of such vibration devices is that the mechanical eccentric motors produce largely uncontrolled vibratory movements which tend to damage and thus cause premature wear on the mold. For this reason, the mold and the vibrating table must be built so as to be very stable and strong and these structures are thus more complex. Moreover, the noise burden from such mechanical vibrating drives is very high and uncomfortable.
Applicant""s copending patent application Ser. No. 09/564,035 filed May 4, 2000 discloses positioning Piezoelectric vibration exciters between the vibrating table and the frame of the mold machine. These exciters have a vibrating frequency and other parameters of the vibration drive which can be electronically controlled according to specific requirements of the particular molding operation. The stationary portion of the vibration exciter is connected to the machine frame and the vibrating portion of the exciter is connected to the vibrating table. Such a structure requires complete re-engineering of the mold machine. Existing mold machines therefore cannot be easily refitted with such piezoelectric vibration exciters.
It is therefore the principal object of the present invention to provide a novel and improved vibration drive utilizing piezoelectric vibration exciters.
It is another object of the present invention to provide such a vibration drive which can be mounted on a vibrating table or mold in a mold machine for producing shaped concrete bodies.
It is a further object of the present invention to provide such a vibration drive which is simplified in structure and which can be mounted directly on the structure which is to be vibrated.
The objects of the present invention are achieved and the disadvantages of the prior art as described above are overcome by the vibration drive of the present invention which has a piezoelement drivingly connected to an unbalance mass which is supported to vibrate freely in the housing of the exciter. The housing is fixedly mounted directly on the mold, the vibrating table or some other structure which is to be caused to vibrate. By applying an AC voltage to the piezoelement it is caused to execute an oscillating movement which is transmitted to the unbalance mass and thus also causes the mold to vibrate.
According to one embodiment of the present invention, the unbalance mass is a piston which is freely mounted of reciprocating movement in a cylindrical space in the housing of the vibration exciter. For damping of the end positions of the moveable piston, at least on the side of the piston opposite the piezoelement there is provided a return valve in the cylinder. The valve opens in the pulling direction of the spring system of the piezoelement and closes in the compression direction in the end position of the piston. Preferably, the return valve is mounted in a cover which closes the cylindrical space within the housing.
In order to produce a vibration movement which is particularly suitable for the different operating positions, at least one vibration exciter with a vertical and/or horizontal direction of vibration is interchangably mounted on one or more sides of the mold. As a modification, the vibration exciter can also be constructed to be an integral portion of the mold itself.
The advantages and results achieved with the present vibration drive is that the vibration exciter can be constructed so as to be relatively small and compact in dimensions and can be attached to various locations in any number on the mold or vibrating table in order to produce different vibrating conditions as may be desired. The vibration exciter can be mounted in such a manner that the vibrating movement of the mold can occur in the vertical or horizontal vibrating directions or there can be a combination of vertical and horizontal vibrations. Mounting the piezoelectric vibration drive directly on the mold significantly reduces the energy consumption since it is only required to vibrate the mold and not other structural members of the machine. Accordingly, the vibration behavior of the mold can be precisely controlled and the noise burden considerably reduced. Since a special vibrating table is not required, the space below the mold can be kept free or may be utilized to insert mold cores or recess bodies from underneath into the mold cavities.
Another major advantage is that in existing mold machines having a vibrating table, the mechanical eccentric motors can be readily and easily replaced by the piezoelectric vibration exciters.